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Income taxes - Additional Information (Detail) (USD $) | 12 Months Ended
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Dec. 31, 2012 | Dec. 31, 2011
Income Tax [Line Items] |  |
Income tax expense | $ 1,395,000 | $ 634,000
Operating loss carryforwards | 11,000,000 |
Operating loss carryforwards, expiration dates | expiring through 2029 |
Operating loss carryforwards, limitations on use | Company's NOLs are subject to annual limitations of $1,300,000 |
State and local income tax expense (benefit), continuing operations | 5,395,000 |
Deferred tax assets | $ 4,000,000 |

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